The gamma-aminobutyric acid type A, GABA (A), receptor mediates the majority of fast synaptic inhibition in the brain and is a target of many depressants, such as the benzodiazipines, barbiturates, and alcohol.The most prevalent receptor subtype contains alpha, beta, and gamma subunits. However, GABA (A) receptors containing the delta subunit, instead of gamma, display a unique sensitivity to ethanol and may play a key role in mediating the behavioral effects of alcohol at physiologically relevant doses. Evidence also indicates that chronic use of alcohol may cause a permanent rearrangement of receptor subtype levels in the brain, which may ultimately result in increased substance dependence and altered receptor pharmacology. Alcoholism and alcohol abuse are serious problems that have severe repercussions on physical and mental health as well as family and lifestyle. 13.8 million American adults have problems with drinking, 8.1 million of which are alcoholic. Chronic alcohol abuse causes major damage to the brain as well as other symptoms requiring extensive medical care that in total costs society billions of dollars each year. Several research groups have shown conflicting results when investigating ethanol sensitivity of GABA (A) delta-containing receptors, and ethanol sensitivity may be dependent on the subunit isoforms present. The proposed research will clarify and further characterize delta-containing receptors by determining their subunit stoichiometry, using alpha4-beta2-delta receptors as a model. The responsiveness of the receptors to low doses of ethanol will be established and the putative ethanol binding site on the receptors will be mapped. The drug Ro15-4513, which is currently used clinically to antagonize the behavioral effects of excessive alcohol consumption, binds with high affinity to delta-containing GABA (A) receptors and is thought to compete for the same binding site as alcohol. Ro15-4513 contains a photo-activatable azido group that will be used to photolabel delta-containing receptors. The specific subunit into which the drug photoincorporates will then be identified and the photolabeled region of the subunit will be narrowed down using a series of proteolytic digestions. The success of this project will provide a better understanding of how GABA (A) receptors mediate the effects of alcohol in the brain and will provide insight that will aid in the development of novel pharmacotherapeutics for the treatment of many symptoms of chronic alcohol abuse. Better drugs are needed to treat alcoholism and alcohol abuse. Alcohol affects the brain by binding to specific proteins called GABA (A) receptors. The proposed research will help identify where alcohol is binding to these receptors and thus will aid in the development of new drugs.